NOCTILUCENT CLOUD SEASON BEGINS: NASA's AIM spacecraft has just spotted electric-blue clouds floating at the edge of space over the Arctic Circle. These are noctilucent ("night-shining") clouds, formed by wisps of summertime water vapor crystallizing around meteor smoke in Earth's upper atmosphere. Soon, observers on the ground should be able to see them, too. Visit today's edition of Spaceweather.com for the latest images and observing tips.
Above: This is what a fully-developed display of noctilucent clouds looks like, photographed on August 5, 2017, by Catalin Tapardel from Alberta, Canada.
